A conveyor of the above type is the subject of U.S. Pat. No. 3,967,720. Therein is disclosed a belt conveyor having at least one straight load bearing section and comprising:
A pair of flexible elementary belts which are each reinforced at least longitudinally by a reinforcing layer embedded in the vicinity of the neutral axis thereof and which each have a regular array of projections and intermediate recesses arranged so that the projections of one belt fit exactly into the recesses of the other belt: and PA1 Belt guide means which provides first curved path portions to progressivley bring said belts together into mutual positive engagement and rigidly interlocked relationship at one end of said straight load bearing section, which support and maintain said belts rigidly interlocked along said straight section, and which further provides second curved path portions to progressively separate said belts beyond the opposite ends of said straight section. PA1 I. the exact engagement of two elementary belts permits the formation of a composite beam presenting a rigidity which is several times higher than that of two belts taken individually or superimposed and connected in any other manner (without exact interengagement); in fact, it becomes possible thereby to temporarily realize, due to such assemblage of a composite unitary beam, on the straight section adapted for the transport of loads, an effect of optimal reinforcement which results from the combined action of the respective reinforcing layers of the two elementary belts. PA1 ii. In return, when the two belts are separated from one another they will present a relatively high flexibility since the reinforcing layer is situated as close as possible to the neutral axis of each belt; thus due to the great flexibility of each separate belt, it is possible to easily obtain any change of direction desired in the travel of the conveyor by conducting the belts along separate curvilinear paths having relatively small radii.
This construction presents very substantial advantages, notably for the transport of heavy loads, namely:
Band conveyors generally require changes of direction more or less substantial over their path and, in particular, reversal of direction at the extremities of the straight section of an endless belt conveyor.
It is therefore, obvious that the changes of direction are also necessary along the path of travel of the belt conveyor according to the present invention and in particular at the two extremities of the said composite beam, namely, on the one hand at the extremity of engagement (by exact interfitting) and on the other hand at the extremity of separation of the two elementary movable belts.
Thus, although the formation of a composite beam, such as that provided according to the prior application has the substantial advantages mentioned hereinabove, the exact interengagement that it necessitates can nevertheless lead to a more or less substantial friction between the mutual contact surfaces of the two elementary belts during their movements of interengagement and of separation. Thus, there is the risk that the friction will lead to a more or less rapid wear of the interengagement surfaces of the two bands.
Moreover, since the speed of the conveyor is preliminarily fixed according to the intended usage, the speed of relative movement which results in the two elementary belts therefrom is also fixed and cannot be reduced as desired in order to reduce substantial friction.
Thus, the wear of the interengaged surfaces of the two elementary belts is of great importance fro the formation of a composite beam according to the present invention since such wear can lead to a play susceptible of cancelling the exact interengagement, thus losing the important advantages mentioned hereinabove.